No matter how you cut it, finding mutant butterflies is hard to spin as a positive result. But the knowledge gained from the pale grass blue butterfly, a.k.a. Zizeeria maha, could potentially help down the road as the country recovers from one of the world’s worst nuclear power disasters.

According to a study published by Scientific Reports, researchers started looking at butterflies near the Fukushima Daiichi nuclear plant two months after the March 2011 tsunami damaged the reactors, causing a potential radiation leak. Of the initial 100 butterflies studied, 12% had mutations. But as the butterflies mated, the rate of mutation in successive generations increased to 34%, showing that the mutating genes were easily passed along to offspring.

The problems were widespread, with abnormalities found including broken or wrinkled wings, changes in wing size, problems with legs, antennae, abdomen and eyes and even shifts in color pattern. Intrigued by the initial findings, researchers took a look at 200 butterflies in September and found that the mutation rate was increasing in the latest generation of butterflies — the ones that were likely larvae around the time of the disaster — with more than half of new butterflies showing some kind of mutation.

The news is obviously troublesome for the entire region, raising concerns about the harmful long-term effects of the Fukushima disaster — the largest since Chernobyl in 1986 — but it also underscores the important role of early-warning signs stemming from radiation leaks.

But butterflies can be particularly susceptible to radiation; not all animals will suffer a similar fate, which is exactly why researchers want more tests done on different species. “Sensitivity [to irradiation] varies between species, so research should be conducted on other animals,” Joji Otaki, an associate professor at the University of the Ryukyus in Okinawa, told the JapanTimes.

Fortunately for humans, they generally fare better than butterflies when it comes to handling radiation. Hopefully much better.

Tim Newcomb is a journalist based in the Pacific Northwest covering sports design and technology, culture, infrastructure and entertainment. He writes for Sports Illustrated, Popular Mechanics, TIME and more.